Unravelling the ion transport and the interphase properties of a mixed olivine cathode for Na-ion battery

The replacement of Li by Na in an analogue battery to the commercial Li-ion one appears a sustainable strategy to overcome the several concerns triggered by the increased demand for the electrochemical energy storage.However,the apparently simple change of the alkali metal represents a challenging step which requires notable and dedicated studies.Therefore,we investigate herein the features of a NaFe_(0.6)Mn_(0.4)PO_(4)(NFMP)cathode with triphylite structure achieved from the conversion of a LiFe_(0.6)Mn_(0.4)PO_(4)(LFMP)olivine for application in Na-ion battery.The work initially characterizes the structure,morphology and performances in sodium cell of NFMP,achieving a maximum capacity exceeding 100 mAh g^(−1)at a temperature of 55℃,adequate rate capability,and suitable retention confirmed by ex-situ measurements.Subsequently,the study compares in parallel key parameters of the NFMP and LFMP such as Na^(+)/Li^(+)ions diffusion,interfacial characteristics,and reaction mechanism in Na/Li cells using various electrochemical techniques.The data reveal that relatively limited modifications of NFMP chemistry,structure and morphology compared to LFMP greatly impact the reaction mechanism,kinetics and electrochemical features.These changes are ascribed to the different physical and chemical features of the two compounds,the slower mobility of Na^(+)with respect to Li^(+),and a more resistive electrode/electrolyte interphase of sodium compared with lithium.Relevantly,the study reveals analogue trends of the charge transfer resistance and the ion diffusion coefficient in NFMP and LFMP during the electrochemical process in half-cell.Hence,the NFMP achieved herein is suggested as a possible candidate for application in a low-cost,efficient,and environmentally friendly Na-ion battery.

Characteristics of a gold-doped electrode for application in high-performance lithium-sulfur battery

Bulk sulfur incorporating 3 wt% gold nano-powder is investigated as possible candidate to maximize the fraction of active material in the Li-S battery cathode.The material is prepared via simple mixing of gold with molten sulfur at 120℃,quenching at room temperature,and grinding.Our comprehensive study reports relevant electrochemical data,advanced X-ray computed tomography(CT)imaging of the positive and negative electrodes,and a thorough structural and morphological characterization of the S:Au 97:3 w/w composite.This cathode exhibits high rate capability within the range from C/10 to 1C,a maximum capacity above 1300 mAh gs^(-1),and capacity retention between 85%and 91%after 100 cycles at 1C and C/3 rates.The novel formulation enables a sulfur fraction in the composite cathode film as high as 78 wt%,an active material loading of 5.7 mg cm^(-2),and an electrolyte/sulfur(E/S)ratio of 5μL mg^(-1),which lead to a maximum areal capacity of 5.4 mAh cm^(-2).X-ray CT at the micro-and nanoscale reveals the microstructural features of the positive electrode that favor fast conversion kinetics in the battery.Quantitative analysis of sulfur distribution in the porous cathode displays that electrodeposition during the initial cycle may trigger an activation process in the cell leading to improved performance.Furthermore,the tomography study reveals the characteristics of the lithium anode and the cell separator upon a galvanostatic test prolonged over 300 cycles at a 2C rate.

Current collectors based on multiwalled carbon-nanotubes and fewlayer graphene for enhancing the conversion process in scalable lithium-sulfur battery

We investigated herein the morphological,structural,and electrochemical features of electrodes using a sulfur(S)-super P carbon(SPC)composite(i.e.,S@SPC-73),and including few-layer graphene(FLG),multiwalled carbon nanotubes(MWCNTs),or a mixture of them within the current collector design.Furthermore,we studied the effect of two different electron-conducting agents,that is,SPC and FLG,used in the slurry for the electrode preparation.The supports have high structural crystallinity,while their morphologies are dependent on the type of material used.Cyclic voltammetry(CV)shows a reversible and stable conversion reaction between Li and S with an activation process upon the first cycle leading to the decrease of cell polarization.This activation process is verified by electrochemical impedance spectroscopy(EIS)with a decrease of the resistance after the first CV scan.Furthermore,CV at increasing scan rates indicates a Li+diffusion coefficient(D)ranging between 10^(−9) and 10^(−7) cm^(2)·s^(−1)in the various states of charge of the cell,and the highest D value for the electrodes using FLG as electron-conducting agent.Galvanostatic tests performed at constant current of C/5(1 C=1675 mA·g_(s)^(−1))show high initial specific capacity values,which decrease during the initial cycles due to a partial loss of the active material,and subsequently increase due to the activation process.All the electrodes show a Coulombic efficiency higher than 97%upon the initial cycles,and a retention strongly dependent on the electrode formulation.Therefore,this study suggests a careful control of the electrode in terms of current collector design and slurry composition to achieve good electrode morphology,mechanical stability,and promising electrochemical performance in practical Li-S cells.

Nanostructured Na-ion and Li-ion anodes for battery application： A comparative overview

This paper offers a comprehensive overview on the role of nanostructures in the development of advanced anode materials for application in both lithium and sodium-ion batteries. In particular, this review highlights the differences between the two chemistries, the critical effect of nanosize on the electrode performance, as well as the routes to exploit the inherent potential of nanostructures to achieve high specific energy at the anode, enhance the rate capability, and obtain a long cycle life. Furthermore, it gives an overview of nanostructured sodium- and lithium-based anode materials, and presents a critical analysis of the advantages and issues associated with the use of nanotechnology.

Physical activation of graphene: An effective, simple and clean procedure for obtaining microporous graphene for high-performance Li/S batteries

Graphe ne nano sheets are a promising scaffold to accommodate S for achievi ng high performa nee Li/S battery. Nano sheet activation is used as a viable strategy to induce a micropore system and further improve the battery performance. Accordingly, chemical activation methods dominate despite the need of multiple stages, which slow down the process in addition to making them tiresome. Here, a three-dimensional (3D) N-doped graphene specimen was physically activated with CO2, a clean and single step process, and used for the preparation of a sulfur composite (A-3DNG/S). The A-3DNG/S composite exhibited outstanding electrochemical properties such as an excellent rate capability (1,000 mAh·g^-1 at 2C), high reversible capacity and cycling stability (average capacity ~ 800 mAh·g^-1 at 1C after 200 cycles), values which exceed those measured in chemically activated graphene. Therefore, these results support the use of physical activation as a simple and efficient alternative to improve the performance of carbons as an S host for high-performance Li-S batteries.